1. Field of the Invention
The present invention relates to a magnetic drive apparatus, and more particularly to a magnetic drive driving apparatus that does not require coil-based driving force.
2. Description of the Related Art
In a magnetic drive driving apparatus, which utilizes magnetic force, current is ordinarily supplied to an excitation coil to generate magnetic force, and this magnetic force rotates a rotor magnet. For example, a stepping motor is one such known magnetic drive driving apparatus. When this magnetic drive driving apparatus is used as the drive source for a clock, for example, it intermittently drives a stepping motor comprising the above-described constitution using reference signals generated via a quartz oscillator (For example, refer to Japanese Patent Laid-open No. 2002-90473 (page 1, FIG. 1)).
In a magnetic drive apparatus that uses an excitation coil such as that mentioned above, applying driving current to the excitation coil generates copper loss. This copper loss is problematic in that it does not allow high energy efficiency, and makes it difficult to reduce power consumption.
Further, in a magnetic drive apparatus that uses an excitation coil, the size of the apparatus is limited by the diameter of the coil and the flux saturation of the magnetic path. Thus, in order to make the magnetic drive apparatus smaller and thinner, it is necessary to decrease the size of the coil diameter, and to make the effective cross section of the magnetic path smaller. However, decreasing the coil diameter lowers torque, and reducing the effective cross section of the magnetic path results in the amount of magnetic flux being limited by flux saturation. Another problem with a magnetic drive apparatus is that it must be of a certain size in order to ensure torque of a prescribed magnitude.
Therefore, it is impossible to ensure torque of a prescribed magnitude in a magnetic drive apparatus while simultaneously striving to make the magnetic drive apparatus smaller and thinner.
As described hereinabove, the problems associated with a conventional magnetic drive apparatus, such as power consumption, restrictions placed on the amount of magnetic flux by flux saturation, and restrictions placed on compactness and thinness by the coil diameter, have their origins in the use of an excitation coil as the driving component.
Accordingly, with the foregoing problems in view, there has been proposed a driving device, which uses a magneto-resistance switching element to start and stop the flow of magnetic flux from a permanent magnet to a stator (Refer to Japanese Patent Laid-open No. 54-126917 (page 3, FIG. 2)).
A magnetic drive apparatus that uses an excitation coil as a driving source, as described hereinabove, is problematic in that using an excitation coil as a driving source results in high power consumption, and the coil diameter limits how compact and thin the magnetic drive apparatus can be made.
To solve for these problems, a driving method for controlling the ON/OFF of magnetic flux using a magneto-resistance switching element instead of a coil drive has been proposed in the above-mentioned Japanese Patent Laid-open No. 54-126917 (page 3, FIG. 2), but the problem with this driving method is that it uses a coil as the magneto-resistance switching element, and is therefore unable to achieve the effects of sufficient power saving, compactness and thinness.
Further, even if a magneto-resistance switching element that does not use a coil is utilized, the constitution proposed in Japanese Patent Laid-open No. 54-126917 (page 3, FIG. 2) is ON/OFF control, which controls whether the magnetic flux of a permanent magnet is allowed to flow to a stator or not, and as such, simply switches the flow of magnetic flux to the rotor in two directions.
Rotating the rotor requires that the direction of flux applied to the rotor be sequentially controlled in accordance with the direction of rotation. However, as mentioned above, control that simply switches the magnetic flux ON and OFF is a problem in that it is not possible to freely change the driving direction of the rotor, and is also problematic from the standpoint that it makes smooth driving control impossible.
Further, the fact that magnetic flux returns to the permanent magnet itself without traveling to the rotor when the magnetic flux is switched is also a problem in that the magnetic flux is not able to contribute to the driving of the rotor, making it difficult to realize high driving efficiency.
Further, it is difficult to fabricate a ferromagnetic material, such as a permanent magnet or magnetostrictive material to precise dimensions, and when a ferromagnetic material is incorporated into a magnetic path, magnetic flux leakage increases even with micro-sized gaps. This is also a problem in that strict dimensional accuracy is required for ferromagnetic materials, making the cost of fabrication and assembly very expensive.
Accordingly, an object of the present invention is to provide a magnetic drive apparatus that solves for these past problems, does not require an excitation coil, lowers power consumption by reducing energy consumption resulting from the copper loss of an excitation coil and so forth, and makes the driving apparatus smaller and thinner.
Further, in addition to the above-mentioned object, another object of the present invention is to provide a magnetic drive apparatus that achieves smooth driving control, and enhances driving efficiency. Yet another object of the present invention is to provide a low-cost magnetic drive apparatus for which strict dimensional precision is not required when using a material that is difficult to fabricate to precise dimensions.